Recognition between biological molecules plays a fundamental role in most processes in living cells. To understand the mode of recognition, it is necessary to know the three dimensional structure of the molecular complex involved at the atomic resolution. Our objectives are: 1. to make single crystals of the molecular complexes between RNA and various interacting molecules, such as aromatic mutagens, aromatic carcinogens, aromatic dyes, basic peptides and oligonucleotids; 2. to determine the three dimensional structure of these molecular complexes using X-ray crystallographic methods; 3. to utilize this structural information to understand the interactions between nucleic acids and aromatic mutagens (or carcinogens), between DNA and histones, between DNA and RNA, between RNA and RNA, and between nucleic acid and protein in general. BIBLIOGRAPHIC REFERENCES: A comparison of the fluorescence of the Y base of yeast tRNA(Phe) in solution and in crystals, by R. Langlois, S.H. Kim, C.R. Cantor. Biochemistry, 14, 2554 (1975). Symmetry recognition hypothesis model for tRNA binding to aminoacyl tRNA synthetase, by S.H. Kim. Nature, 256, 679 (1975).